Archaeologists believe they have solved one ancient mystery surrounding the famous Easter Island statues.

At 2,500 miles off the coast of Chile, the island is one of the world's most remote places inhabited by people.

Up to 1,000 years ago, the islanders started putting giant red hats on the statues.

The research team, from the University of Manchester and University College London, think the hats were rolled down from an ancient volcano.Dr Colin Richards and Dr Sue Hamilton are the first British archaeologists to work on the island since 1914.

They pieced together a series of clues to discover how the statues got their red hats. An adze, a road, and an ancient volcano led to their findings.Dr Richards said: "We know the hats were rolled along the road made from a cement of compressed red scoria dust."

Each hat, weighing several tonnes, was carved from volcanic rock. They were placed on the heads of the famous statues all around the coast of the island.

However, precisely how and why the hats were attached is unknown.Like an altar. An adze was found in pristine condition next to the hats. The scientists think it might be an ancient offering.

A ceremonial adze was found next to the hats Dr Richards told BBC News: "These hats run all the way down the side of the volcano into the valley.

"We can see they were carefully placed. The closer you get to the volcano, the greater the number.

"It's like a church; you can't just walk straight to the altar."The Polynesians saw the landscape as a living thing, and after they carved the rock the spirits entered the statues."

Dr Richards and Dr Hamilton are joint directors of the "Rapa Nui (Easter Island) Landscapes of Construction Project". They will be working on the island over the next five years.

It's also interesting to note that some of the stone platforms that these statues sit on are built with large polygonal stones that fit together like a jigsaw puzzle... in the same style of the so-called Inca stonework such as can be seen in Cuzco, Sacsayhuaman, Ollantaytambo and Machu Picchu in Peru...

Stepping off the plane, tourists are welcomed to Easter Island with a garland of flowers. They find themselves on a tiny dot in the Pacific Ocean, 3,700 kilometres west of Chile, to which the island belongs, and 2,000 kilometres east of Pitcairn Island. All around are the white-flecked waves of the Pacific. "What perfect peace," exclaimed Thor Heyerdahl, a Norwegian explorer when he arrived in the mid-1950s.

He might not say so today. Some 70,000 visitors now arrive each year, up from just 14,000 in the mid-1990s. Apart from the island's utter remoteness, what attracts the tourists are the moai, the mysterious giant stone statues erected by the ancestors of the indigenous Rapa Nui people. They are a testament to a complex society of up to 20,000 people that later shrank to a shadow as a result of calamitous environmental stress and deforestation, a cautionary tale narrated in Collapse, a book by Jared Diamond, a polymath at the University of California.

Today, Easter Island once again faces environmental threats. Food comes from Chile, either by ship or on the seven weekly flights from Santiago (there are also two from Tahiti). The visitors "all pull the chain," Luz Zasso, the mayor, notes acidly. The absence of a sewage system is threatening the cleanliness of the island's underground water sources. But it would be hard to install one without damaging archaeological sites. Electricity comes from diesel-powered generators. Power cuts are frequent. Trash is piling up.

Many Easter Islanders are worried. Tourists should be limited to 50,000 a year and be preferably well-heeled, argues Marcelo Pont, the vice-president of the Council of Elders, an advisory body. Visitors from the Chilean mainland attract particular resentment.

"They're interested in sun, sand and swimming pools, not the island," says Edgard Herevi of the local chamber of tourism. Tourism has brought migrants from the mainland, too. The population is now 5,000, up from 3,300 in 2002, of whom only half are of Rapa Nui descent. Locals complain that the incomers are competing in the handicrafts trade, carving wooden moai and selling shell necklaces.

There is almost no unemployment, and thanks to tourist revenues and government spending, living standards are similar to those on the mainland. But locals worry about the future. In response, Chile's government is proposing laws that would beef up the island's government, give the Rapa Nui more say in it and allow them to control immigration. It also plans to raise the entrance fee to the Rapa Nui National Park, where most of the main sights are, from $10 to $60 for foreigners.

The Rapa Nui Parliament, a radical group that split from the Council of Elders, is calling for independence. Its supporters blocked the airport's runway for two days in August. It wants to expel Chileans, even those who have lived much of their lives on the island, unless they have a long-standing relationship with a Rapa Nui or are the parent of a child with Rapa Nui blood.

The group also dreams of ditching Chile's peso and forming a Polynesian currency union, including Australia.

Such claims are merely a sign of economic frustration, argues Sergio Rapu, an archaeologist and former governor of the island. Perhaps. But the question they raise is whether greater autonomy to run their own affairs would help the Rapa Nui to avoid a repeat of the ecological collapse they failed to prevent centuries ago.